The purpose of this project is to study the biochemical events associated with plasticity in the nervous system. Protein synthesis is a biochemical process which is involved in bringing about changes in morphology, adjustments in growth rates, and remodeling and maintenance of structure and function. We have, therefore, used the quantitative autoradiographic [1-14C]leucine method to study the site of origin and the process underlying the reorganization. Similarly, we have used the [14C]deoxyglucose method to examine the outcome of the plastic changes, i.e. the functional reorganization that has occurred. We are studying two model systems: (a) the developing monkey visual system, and (b) the developing and adult mouse somatosensory system. Studies of chronic monocular deprivation in monkeys early and late in the critical period were carried out to examine the response of the lateral geniculate cells to deprivation. Our results show that at both time points, early when there is considerable overlap and late when input to each column is almost exclusively from the dominant eye, the biochemical response that may underlie the functional reorganization of the striate cortex is a decrease in the rate of protein synthesis indicative of a decrease in the growth rate in the deprived geniculate cells. Preliminary results of studies of whisker follicle lesions in adult mice suggest that there is functional reorganization in the cortical barrel field and that this system may serve as a useful model of adult plasticity.